The European Union (EU) is a political and economic union of twenty-seven member states, located primarily in Europe. It was established in 1993 as a result of the signing of the Treaty on European Union (otherwise known as the Maastricht Treaty), adding new areas of policy to the existing European Community. With almost 500 million citizens, the EU combined generates an estimated 30% share of the world's nominal gross domestic product.

The EU has developed a single market through a standardised system of laws which apply in all member states, guaranteeing the freedom of movement of people, goods, services and capital. It maintains a common trade policy, agricultural and fisheries policies, and a regional development policy. Fifteen member states have adopted a common currency, the euro. It has developed a role in foreign policy, representing its members in the World Trade Organization, at G8 summits and at the United Nations. Twenty-one EU countries are members of NATO. It has developed a role in justice and home affairs, including the abolition of passport control between many member states under the Schengen Agreement.

EU operation is a hybrid of intergovernmentalism and supranationalism. In certain areas it depends upon agreement between the member states. However, it also has supranational bodies, able to make decisions without the agreement of members. Important institutions and bodies of the EU include the European Commission, the European Parliament, the Council of the European Union, the European Council, the European Court of Justice and the European Central Bank. EU citizens elect the Parliament every five years.

The EU traces its origins to the European Coal and Steel Community formed among six countries in 1951 and the Treaty of Rome in 1957. Since then the EU has grown in size through the accession of new member states and has increased its powers by the addition of new policy areas to its remit. The Treaty of Lisbon was signed in December 2007 with the intention to amend the existing treaties to update the political and legal structure of the union. The ratification process was scheduled to be accomplished by the end of 2008; however the rejection of this treaty in the Irish referendum of June 2008 has left its future unresolved.